The invention is directed to a method for contacting conductive structures in VLSI circuits in a vacuum chamber with the assistance of laser light.
It is frequently necessary in semiconductor technology to undertake micro-work at a semiconductor substrate during the manufacture of integrated circuits on a semiconductor substrate. These include, among other things, the local removal of passivation or insulating layers in circuits metallized in one-layer or multi-layer fashion with the goal of making conductive structures such as, for example, interconnects or pads accessible for various purposes. Such purposes, for example, are analyses of electrical measuring and testing purposes. Furthermore, the locally exposed interconnects can be electrically conductively connected to one another by metal deposition in order, for instance, to implement design modifications in a simple way and to check their compatibility. Semiconductor modules can also be repaired in the same way. It is important in all of these purposes to produce a good electrical contact to the exposed, conductive structure.
When the insulating layer to be eroded is composed of silicon nitride or of an organic material such as, for example, polyimide, then it can be locally removed on the basis of what is referred to as ablation with the assistance of a pulsed UV laser, wherein the laser beam is directed or focused onto the desired location. Such an ablation, however, is not possible given an insulating layer having a high UV-transmission such as, for example, silicon oxide and other glass-like layers, since the layer lying therebelow would be damaged by the intense UV radiation. A number of laser-induced etching processes are known for the local removal of silicon oxide layers and are described in the article by G. Loper and M. Tabat in SPIE Vol. 459, Laser Assisted Deposition Etching and Doping (1984), pages 121-124, incorporated herein. Such laser-induced etching processes are based on the defined production of highly reactive radicals of halogen-carbon compounds with the assistance of pulsed UV lasers in a vacuum chamber, so that a chemical reaction of the silicon oxide with these radicals occurs upon formation of volatile silicon and oxygen compounds. The gaseous chlorine or fluorine compounds employed, however, have high toxicity and have an extremely corrosive effect on many materials, so that a high technological expenditure is required. Mechanical parts situated in the vacuum chamber such as, for example, xyz-tables for the exact positioning of the semiconductor substrate to be processed, become unusable due to corrosion within a short time. The exposed conductive structures often have surfaces that do not meet the demands made for a good electrical contact. In particular, an oxidation in air can generally not be prevented before, for example, metal is deposited thereon or before measuring tips are put in place.